WEATHER: Flash Flood Watch until Midnight

Posted at 1:10 PM, Jul 21, 2012
and last updated 2012-07-21 14:52:45-04

RICHMOND, Va. (WTVR) – Far southeast Virginia will be most favored for strong thunderstorms Saturday afternoon and evening, along and southeast of a stalled boundary that moved into the Commonwealth Friday. The air-mass in Virginia remains quite moist with high precipitable water values (i.e., there’s plenty of moisture to rain out and produce local heavy downpours). Storm motion with this stalled boundary is slow, as well, so that can add to the heavy rainfall threat in any one location because one storm may continue to rain heavily over the same location for a while as it drifts along. Rainfall rates could range a half an inch to an inch per hour. As a result of the heavy rainfall potential, a Flash Flood Watch will be in effect until Midnight for all of the areas highlighted in green on the above map, which does not include the City of Richmond, but does cover most of south-central, parts of east-central, and southeast Virginia. As much as 2″ to 4″ of rainfall is possible from heavy thunderstorms through this evening. These are slow-moving storms along a stalled surface boundary, with ample moisture in the atmosphere to precipitate (rain) out. Driving in these heavy downpours can be dangerous as visibilities can drop below a quarter of a mile. Be sure to turn on your hazard lights and slow down if you have to drive through these downpours. This will help other drivers to see you better!

The updated Slight Risk map issued mid-day from the Storm Prediction Center highlights far southeast Virginia for a greater wind damage threat, and into the North Carolina. 

If you look specifically at the area of greatest wind damage potential, it’s where there has been less cloud-cover the first half of the day (for better heating and instability).  For example, here is the latest visible satellite image (as of this posting) of our region. You can see a cumulus field over the Carolinas into far Southeast Virginia. That indicates rising moisture and potentially storm development this afternoon. However, most of central, northern and west-central Virginia has been socked in under cloud-cover and morning showers, limiting heating and instability.

After seeing that, the temperature spread across the region mid-day has been influenced by that morning cloud-cover and rain, with the best heating closer to the North Carolina state line and far southeast Virginia. Temperatures as of this posting are in the low 80s in Southeast Virginia, as compared to Northwest Virginia holding in the mid to upper 60s! 

The stalled boundary is draped approximately from west to east across Southern Virginia, and will serve as a focus for enhanced rainfall while it lingers there.  The primary threat with any showers and storms that develop today will first of all be the potential for local heavy rainfall that can lead to flash flooding, especially in areas that have already received heavy rainfall the past couple of days. Any severe thunderstorms that reach that intensity will be capable of damaging wind gusts in excess of 60 mph.

With plenty of outdoor activities this evening, including outdoor concerts, be prepared to move indoors should a storm threaten your location. Even if it is not severe, there will be the potential for lightning and downpours, as well as gusty winds.

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